The present invention provides an apparatus and method for producing a slurry from a slurry concentrate in which the slurry concentrate, de-ionized water and an oxidizer are pumped into a junction to produce the slurry. More particularly, the present invention relates to such an apparatus and method in which the homogeneity of the slurry is enhanced by passing the slurry through a mixing device and recirculating part of the finished slurry back to the junction.
Slurries are used in a variety of surface treatment techniques. An important surface treatment, used in the manufacture of semiconductor devices, is chemical mechanical polishing or planarization. Typically, slurries used in such surface treatment comprise potassium hydroxide, silicon oxide, an oxidizer such as hydrogen peroxide, and a diluent such as de-ionized water. Ferric nitrate or chloride might also be present. The oxidizer contained within the slurry acts on the surface to be treated and the abrasive particles sweep the surface layer away. Slurries are often shipped to a site as a slurry concentrate that contains, for instance, the potassium hydroxide and silicon dioxide. The diluent and oxidizer are then added to the concentrate at the site or in some instances at the tool itself.
There are however, many difficulties involved in the mixing of the slurry and the handling of the finished slurry, once mixed. One major problem is that the slurry has a very limited pot life and as such, there exists only a limited amount of time to use the slurry after having been mixed. Additionally, slurries such as those used in the semiconductor industry do not remain homogenous upon being subjected to shear forces. For instance, shear induced in the slurry due to sharp pipe bends will produce agglomeration which will destroy the usefulness of the slurry in the semiconductor manufacturing process.
Because of such problems, slurry delivery and mixing systems have been proposed in which the slurry is mixed on site from the slurry concentrate. An example of such a system is disclosed in U.S. Pat. No. 5,407,526. In this patent, the slurry concentrate and oxidant are pumped into a mixing chamber where they are mixed to form the finished slurry. The slurry is then immediately deposited onto the semiconductor so that it can be worked by the polishing tool. Another slurry mixing system is disclosed in U.S. Pat. No. 5,478,435 in which slurries are pumped directly onto a polishing pad of a chemical mechanical planarization tool.
In each of the foregoing patents, the mixing of the slurry from the slurry concentrate can only occur when the polishing tool is in operation. As will be discussed, the present invention provides an apparatus and method in which the slurry is mixed at a location that is remote from the polishing tool to allow for distribution of the slurry to several tools, each of which do not have to be operating. Furthermore, the present invention allows for greater control over the consistency and makeup of the slurry than is possible in either of the foregoing patents.